In the telecommunications field, particularly in long distance networks, long distance network providers continually strive to increase the traffic carrying capability of their transmission medium. For example, since fiber optic cables have increased bandwidth over known twisted pair or copper wire cables, fiber optic cables are used increasingly for connecting network stations and other network elements. As a result, a greater number of stations or network elements can be connected over a fewer number of fiber optic cables, as opposed to prior cables. In other words, each fiber optic cable can handle numerous trunks, as opposed to prior cables.
Unfortunately, if one or more of the fiber optic cables fail, massive disruption of services to a large number of network customers and users can result. Network service providers or telecommunications carriers therefore strive to quickly and economically restore traffic effected by these disruptions or "outages." Restoring network outages generally requires four steps: (1) detecting the network failure, (2) isolating the location of the failure in the network, (3) determining a traffic restoral route, and (4) implementing the restoral route. Network restoration must be executed quickly to ensure minimal interruption of network traffic. Therefore, nearly all telecommunications carriers wish to restore traffic within a few seconds or less. The telecommunications carriers typically restore the highest priority network elements first, and as many of such elements as possible within a short period of time.
Often, multiple transmission systems, such as optical fibers, are combined or bundled and positioned along a common geographic or physical path. For example, many optical fibers are typically bundled into a single cable, which is buried underground between two nodes. Each of these optical fibers supports multiple trunks in a network. For example, each optical fiber can be a separate DS-3 level trunk, which can support 672 separate DS-0 level trunks.
The optical fibers or other transmission systems can suffer from outages caused by numerous events, such as fire, construction equipment, water pressure, animals, etc. While an outage may impact one fiber in a cable bundling multiple fibers, it may not immediately impact other fibers in that same cable. For example, repeated freezing and thawing of water which has seeped into the cable can cause a few, and then several, fibers to suffer intermittent or total outages over a span of several months. As another example, a fire may slowly burn through the cable, sequentially causing outages in each fiber as the fire burns through the cable, where each fiber suffers an outage at distinct intervals of time. As a result, when a given optical fiber in a cable suffers an outage, other fibers in the same bundle will likely also suffer from an outage thereafter.
When a failure occurs in the network, a network restoration system receives numerous alarms for each failed trunk on a failed transmission system (e.g., on an optical fiber). Each node traversed by a failed trunk produces an alarm, and as noted above, multiple trunks often fail as optical fibers fail. Since each trunk in the network typically traverses multiple nodes, the network typically produces numerous alarms from multiple nodes as a result of a failure. However, another optical fiber bundled with the failed optical fiber could at a given moment not yet be impacted, and therefore not generate alarms. Therefore, while numerous alarms are generated at a given moment, sometime thereafter, after other optical fibers fail, the network will produce even more numerous alarms. Because other optical fibers bundled with the first failed optical fiber will also likely fail, the network restoration system should not use any trunks bundled with the first failed optical fiber for restoral routes. Instead, the network restoration system should look for other trunks to use as restoral routes, preferably trunks along physically diverse paths.
The information of physically diverse paths, however, is not readily apparent in network topology data. To determine where in the network a failure has occurred, a central location performs numerous algorithms to apply or correlate various alarms generated in response to the failure with each corresponding trunk in the network topology. The computer or analyst then matches the alarms to physical network topology to isolate the location of the failure within the network, and thereby locate the physical path of the failed trunk. Thereafter, the analyst can locate a physically or geographically diverse path as a restoral route.
For example, if the network restoration system employs DS-3 trunks, the network topology data will likely reflect only nodes in which DS-3 trunks are switched, such as nodes containing DS-3 Digital Cross-Connects (DXC 3/3). The network topology data will likely not reflect intervening nodes, which serve as pass-through nodes for DS-3 trunks. Thus, two DS-3 trunks may be physically diverse by virtue of different intervening, pass-through nodes, but since they share the same DXC 3/3 end nodes, they appear in the network topology data to share the same physical path.
As a result, when a failure occurs and the network restoration system correlates the alarms with the network topology data, the system must analyze the topology data for the entire network. In other words, the network restoration system must analyze the network topology data at various levels, and throughout the network, to determine which spare routes have paths that are physically diverse from the failed path. Such an analysis requires extensive processing, particularly because it typically includes analyzing network topology data at levels lower than the DS-3 level to ensure that all intervening nodes are considered. Such extensive processing necessarily requires processing time, and therefore increases the delay in restoring the network following the failure. As noted above, telecommunications carriers desire to restore outages in the network as quickly as possible.
After isolating the failure, the analyst then identifies an appropriate pre-plan. Currently, telecommunications carriers simulate possible failures and determine restoral routes to develop a "pre-plan" by collecting large amounts of data reflecting the logical topology of the network. The collected data is often retrieved from network engineering databases which reflect the logical construction of the network, such as indicating the connections and paths of all network traffic trunks. An engineer or network analyst analyses the collected data, compares the collected data to the geographic or physical layout location of the network, and then generates the pre-plans therefrom. Since the pre-plans are developed prior to any failure in the network, when a failure does occur, a plan already exists for restoring traffic affected by the failure. In general, a pre-plan corresponds to a segment of the network that can incur a failure. If that segment fails, then the corresponding pre-plan is retrieved, and its restoral route implemented. Since most telecommunications networks are complex, substantial time-consuming processing is required to analyze all of the logical topology data for each node-to-node span of each trunk and determine a restoral route.